Nerve growth factor has been shown to be crucial for the differentiation of several neural lines including sympathetic neurons, adrenal chromaffin cells and the rat pheochromocytoma cell line, PC12. The second messenger(s) for nerve growth factor has (have) not yet been identified. Presented here is preliminary evidence that in PC12 cells nerve growth factor increases by four-fold a protein kinase activity which we have tentatively identified as Casein Kinase II. This effect is specific for nerve growth factor since epidermal growth factor, another hormone which causes the phosphorylation of many of the same proteins as does nerve growth factor, does not influence this casein kinase activity. Furthermore, work presented in this proposal (1) demonstrates that dexamethasone completely inhibits this nerve growth factor-induced increase in casein kinase activity and that (2) this steroid-regulated kinase modulation parallels the dexamethasone inhibition of nerve growth factor-induced neurite outgrowth in PC12 cells. These data are the first reports of any hormonal regulation of this protein kinase. Since it has been demonstrated that microinjection of either the ras or the src oncogene protein kinases can induce differentiation in this cell line, the nerve growth factor/dexamethasone regulation of this casein kinase may be a natural mechanism by which PC12 differentiation is regulated. Through the use of the several different approaches outlined below, the single goal of this project is to determine if the nerve growth factor/dexamethasone regulation of this casein kinase activity is independent of, or inextricably linked to, morphological differentiation. The aims of the proposed studies are to (1) determine the identity of this casein kinase activity, (2) use established neurite- promoting and neurite-inhibiting agents to determine if the nerve growth factor/dexamethasone regulation of this casein kinase is mimiced by other compounds which are known to regulate PC12 differentiation; (3) through the use of microinjection techniques, determine if there is a link between the nerve growth factor/dexamethasone regulation of this casein kinase activity and morphological differentiation; and (4) determine if there is a similar nerve growth factor/dexamethasone regulation of this casein kinase activity in chromaffin cells, another cell type whose differentiation pathways are determined by these two hormones.